3-D object creation system using multiple materials in multiple layers

ABSTRACT

A three dimensional object creation system that prints objects layer by layer, the system including a plurality of printheads, the system printing at least part of each of multiple layers simultaneously, wherein the printheads are configured such that at least one of the layers may be printed with a first set of materials and at least one other of the layers may be printed with a second set of materials, and wherein the first and second sets are not the same.

FIELD OF INVENTION

[0001] This invention relates to the creation of objects using digitaladditive manufacturing and more particularly to creating working objectsthat may be electrically and/or mechanically active.

CO-PENDING APPLICATIONS

[0002] Various methods, systems and apparatus relating to the presentinvention are disclosed in the following co-pending applications filedby the applicant or assignee of the present invention simultaneouslywith the present application:

[0003] DAM01US, DAM02US, DAM03US, DAM05US, DAM06US, DAM07US, DAM08US,DAM09US, DAM10US, DAM11US, DAM12US, DAM13US, DAM14US.

[0004] The disclosures of these co-pending applications are incorporatedherein by cross-reference. Each application is temporarily identified byits docket number. This will be replaced by the corresponding USSN whenavailable.

BACKGROUND

[0005] Digital additive manufacturing is a process by which an object isdefined three dimensionally by a series of volume elements (hereinafterreferred to as voxels). The object is then produced by creating/layingdown each voxel one at a time, in rows at a time, swaths at a time orlayers at a time.

[0006] There exists systems that use modified inkjet type technology to‘print’ material onto a substrate, so building the object. However,these systems typically utilize a single scanning printhead and are onlyuseful for producing non-working models.

SUMMARY OF INVENTION

[0007] In the present invention we digitally define objects as a seriesof voxels and have a production line that creates objects by creatingeach voxel. The production line simultaneously creates differentportions of objects with each portion produced by a separate subsystem.In the preferred embodiments each portion is for different products andso the system builds up multiple objects simultaneously. The finishedobjects may be of identical or of different designs. The portions may beof any shape that may be digitally described. Portions produced bydifferent subsystems may have different shapes.

[0008] In the preferred embodiments each and every voxel has the samedimension. However, a product may be defined by voxels of more than onesize.

[0009] The portions are preferably created or laid down onto one or moresubstrates. In the preferred embodiments one or more substrates areprovided, each having a substantially planar surface upon which materialis deposited. Each of the surfaces preferably moves in it's own planepast the subsystems but does not otherwise move relative to thesubsystems. Each substrate need not have a planar surface upon whichmaterial is deposited and the surface may be of any shape desired. Thesubstrate may move past the subsystems at a constant velocity along apath or may move in steps. The substrate may also be caused to rotateabout one or more axes, as it moves between subsystems, as it moves pastsubsystems, as it is stationary or in combinations of these. In thepreferred embodiments a continuous substrate moves past the subsystemsof the production line at a substantially constant velocity.

[0010] The portions of the object produced by successive subsystemspreferably lie on top of each other but could be spaced apart from eachother, positioned end on end, adjacent to each other or in any otherconfiguration. As an example, a substrate having a cylindrical surfacemay be caused to rotate about its axis as it moves past a subsystem, sothat material deposited extends in a helix on the cylindrical surface.

[0011] The portions are preferably layers of the object and the layersare preferably two dimensional, i.e. they lie in a flat plane. However,the layers need not be planar. The layers may have a constant thickness.Layers having differing thickness within the one layer are within thescope of the invention. Similarly objects may be made with multiplelayers that do not have the same thickness characteristics.

[0012] In the preferred embodiments each layer is planar, is made up ofvoxels of constant size and all layers have the same dimensions.Alternate layers may be offset relative to each other. Preferablyalternate layers are offset by half a voxel in one or both of twomutually orthogonal directions.

[0013] Because voids may be formed in the object, when we refer to a‘layer’ we mean a layer as defined, which may include voids, not acontinuous layer of material or materials.

[0014] In preferred embodiments each layer is created by one or moreprintheads. In the preferred embodiments the printheads are arrangedalong a longitudinally extending production line and one or moresubstrates move past the printheads, and apart from the first layer, theprintheads print onto a previously printed layer of material(s). Theprintheads for all layers operate simultaneously and so whilst the firstprinthead is printing a first layer of a first set of one or moreproducts, the second printhead is printing a second layer of a secondset of one or more products and the third printhead is printing a thirdlayer of a third set. Thus if we have a product 1000 layers high we have1000 different subsystems, one for each layer. These 1000 subsystemsoperate to simultaneously produce 1000 different layers of 1000 sets ofproducts.

[0015] In the preferred embodiments the printheads extend across thewidth of the substrate and are capable of printing across the fullsubstrate width simultaneously i.e. they do not scan or raster whenprinting but are stationary. This enables a substrate to be moved pastthe printheads at a substantially constant speed, with the printheadsprinting rows of material onto the substrate. The substrate speed ismatched to the row width and printhead cycle time so that the substratehas moved the width of the rows printed for each printhead cycle. Thusthe next row or rows printed by each printhead will be printed next to apreviously printed row or rows. In the preferred embodiments theprintheads each print two rows simultaneously for increased substratespeed.

[0016] Whilst substrate width printheads are preferred, scanning typeprintheads may be utilized to simultaneously produce multiple layers ofobjects.

[0017] The terms “printhead”, “print” and derivatives thereof are to beunderstood to include any device or technique that deposits or createsmaterial on a surface in a controlled manner.

[0018] Each layer is printed by one or more printheads. We refer to theprinthead or printheads for a layer as a ‘layer group’. As used in thedescription and claims it is to be understood that a layer group mayhave only one printhead that prints one material and the use of “group”is not to be taken to require multiple printheads and/or multiplematerials.

[0019] Whilst the layer groups may have multiple printheads, each layergroup preferably prints only one layer at any one time, which may bemade of one material or multiple materials. The number of printheads ineach layer is usually determined by the number of materials to beprinted. In the preferred embodiments each material is printed by aseparate printhead and any additional printheads are only to enable asingle layer to have multiple materials within it. This is because thematerials being printed have a relatively high viscosity compared towater based inks and so require large supply channels. Thus in thedescription it is assumed that each printhead only prints one material.Thus if the system is capable of printing N different materials, at oneprinthead per material, this requires N printheads per layer. However,this is not to preclude printheads that print multiple materials.

[0020] However, because each printhead could print more than onematerial or multiple printheads could print the same material, theredoes not have to be a one to one ratio between the number of printheadsand the number of different materials. It is not critical that all thelayer groups are identical, and in some embodiments it is desirable thatdifferent layer groups print different numbers of materials or differentcombinations of materials.

[0021] It will be appreciated that for production efficiency more thanone printhead in a layer group may print the same material. Where therefill rate of the printheads for different materials is substantiallythe same, speed increases can only be achieved when all materials havethe same number of printheads. However if one material requires a muchlonger refill time, provision of two or more printheads for thatmaterial alone may allow increased substrate speed.

[0022] When different materials are printed, they may need to be printedat different temperatures and so in preferred embodiments the printheadsof a layer group may be maintained at different temperatures.

[0023] Even if only one material is used there are advantages inprinting material compared to molding. For example, it is possible tocreate voids in the finished product. The voids may be of any complexitythat may be digitally described. Thus, any pattern of dots may bemissing from the object created.

[0024] The number of separate products that may be printedsimultaneously depends on the printhead width, the product size acrossthe substrate, the product size along the substrate and the longitudinalspacing between products.

[0025] The preferred systems are capable of printing most materials thatare required but there are circumstances where a discrete object may beincorporated into products. Examples of such discrete objects includesemiconductor microchips, which can be manufactured in more appropriatematerials and in much smaller feature sizes than in the current systemsof the invention. For semiconductor devices, the device speed isdependant on feature size and materials used. Whilst preferredembodiments of the invention can produce organic semiconductors, theseare relatively slow compared to conventional inorganic semiconductors.Thus, for example, where a high speed integrated circuit is required,insertion of a separately manufactured integrated circuit chip will beappropriate, as opposed to printing a low speed circuit. Mechanicallyactive objects may also be inserted where printing cannot satisfactorilyproduce them. In embodiments that create three dimensional products, theprinting process may create the cavities into which such discretedevices may be inserted.

[0026] The material(s) printed by the printheads may be hot melts.Typical viscosities are about 10 centipoise. The materials that may beprinted include various polymers and metals or metal alloys. It is thuspossible to print wires, in both two and three dimensions in products.The material solidifies to a solid, either by freezing or by otherprocessing to form solid voxels. As used in the description and claimsthe terms cured, curing or derivatives are to be understood to includeany process that transforms material or materials in one state to thesame or different material or materials in a solid state. Differentmaterials may require different curing techniques or curing conditions.

[0027] The preferred printhead is a Micro Electro Mechanical System(MEMS) type printhead in which a material is ejected from a chamberunder the control of a movable element. Reference is made to thefollowing patent specifications that disclose numerous such MEMS typeprintheads or printhead components: 6,227,652 6,213,588 6,213,5896,231,163 6,247,795 6,394,581 6,244,691 6,257,704 6,416,168 6,220,6946,257,705 6,247,794 6,234,610 6,247,793 6,264,306 6,241,342 6,247,7926,264,307 6,254,220 6,234,611 6,302,528 6,283,582 6,239,821 6,338,5476,247,796 6,557,977 6,390,603 6,362,843 6,293,653 6,312,107 6,227,6536,234,609 6,238,040 6,188,415 6,227,654 6,209,989 6,247,791 6,336,7106,217,153 6,416,167 6,243,113 6,283,581 6,247,790 6,260,953 6,267,4696,273,544 6,309,048 6,420,196 6,443,558 6,439,689 6,378,989 09/425,4206,634,735 6,623,101 6,406,129 6,505,916 6,457,809 6,550,895 6,457,8126,428,133 6,390,605 6,322,195 6,612,110 6,480,089 6,460,778 6,305,7886,426,014 6,364,453 6,457,795 6,595,624 6,417,757 6,623,106 10/129,4336,575,549 6,659,590 10.129,503 10/129,437 6,439,693 6;425,971 6,478,4066,315,399 6,338,548 6,540,319 6,328,431 6,328,425 09/575,127 6,383,8336,464,332 6,390,591 09/575,152 09/575,176 6,322,194 09/575,177 6,629,74509/608,780 6,428,139 6,575,549 09/693,079 09/693,135 6,428,142 6,565,1936,609,786 6,609,787 6,439,908 09/693,735 6,588,885 6,502,306 6,652,07110/302,274 10/302,669 10/303,352 10/303,348 10/303,433 10/303,31210/302,668 10/302,577 10/302,644 10/302,618 10/302,617 10/302,297 MTB001MTB02 MTB03 MTB04 MTB05 MTB06 MTB07 MTB08 MTB09 MTB10 MTB11 MTB12 MTB13MTB14

[0028] Some applications have been temporarily identified by theirdocket number. These will be replaced by the corresponding USSN whenavailable.

[0029] Such MEMS type printheads may utilize different ejectionmechanisms for different ejectable materials while other MEMS printheadsmay utilize different movable shutters to allow different materials tobe ejected under oscillating pressure. It is to be understood thatwhilst MEMS type printheads are preferred, other types of printhead maybe used, such as thermal inkjet printheads or piezoelectric printheads.

[0030] The aforementioned patents disclose printhead systems forprinting ink, but it will be appreciated that the systems disclosed maybe modified to print other materials.

[0031] In the preferred embodiments the data for each layer is stored inmemory on or in or associated with the layer group that prints thatlayer. Preferably each layer group also stores data relating to at leastthe preceding layer. Thus if an earlier layer group fails, successivelayer groups can all, synchronously, change to printing the respectivepreceding layer.

[0032] Preferably, after such a change in which layer(s) a layer groupor groups are printing, the system may automatically transfer layer datafrom one layer group to another so as to restore the layer groups tohaving data relating to at least the preceding layer compared to theactual layer being printed.

[0033] In the preferred embodiments each voxel has dimensions in theorder of 10 microns, each layer of the products is about 10 microns highand in a typical system we have about 1000 separate sub-systems, eachcreating a separate layer of separate items. Thus products up to about 1cm high may be created on a typical production line of the preferredembodiments.

[0034] Each printhead nozzle ejects a droplet that forms, when frozen,dried or cured, a volume element (Voxel) that is approximately 10microns high. The printheads typically print up to about 30 cm in widthand so print up to about 30,000 droplets in each line across thesubstrate. In the preferred embodiments the voxels are treated as beinghexagonal in plan view with an effective height of about 10 microns.

[0035] If we have a system with 1000 layer groups, each of which iscapable of printing 30,000 voxels transversely and 60,000 voxelslongitudinally, we have a volume of 1800,000,000,000 voxels. Within thatvolume we can define as many or as few different products as we desirethat will fit in that volume. Where multiple products are defined withinthat volume, their design need not be the same. We could, for example,define 1000 products within the volume, each with its own differentdesign. Products may be located transversely, longitudinally andvertically relative to other products. Thus products may be created ontop of each other, not just side by side or end on end.

[0036] The preferred embodiments have a print width of about 295 mm, asubstrate speed of about 208 mm and an ability to print about 1000layers, each of which is about 10 microns thick. Thus the preferredembodiments are able to print products that have a thickness up to about1 cm and one of the height and width no more than 295 mm. The other ofthe height and width may be up to about 600 mm. As will be explainedlater, this dimension is limited by memory considerations.

[0037] Product Samples

[0038] Examples of products that may be manufactured using embodimentsof the invention include small electronic devices, such as personaldigital assistants, calculators through to relatively large objects,such as flat panel display units. The productivity of a production lineis exemplified by the following examples.

[0039] Personal Digital Assistant

[0040] An example product that may be produced by a system of thepresent invention is a personal digital assistant (PDA) such as thosemade by Palm Inc of Milpitas, Calif. USA. A typical PDA has dimensionsof 115 mm×80 mm×10 mm (H×W×D). Using hexagonal voxels 10 microns highand with a side length of 6 microns, a total of about 98 billion voxelsare required to define each product. This requires approximately 98Gbytes of data, if we assume that eight different materials are used inthe product.

[0041] At a substrate speed of 208 mm per second a typical productionline can produce approximately 4.32 products per second, 373151 productsper day or 136 million products per year, assuming the system runscontinuously. Whilst this is greater than the current market for suchproducts, the system has the potential to substantially reduce the costof these products and so increase the market.

[0042] Whilst the system may print polymer transistors and displays,these have lower performance than silicon based transistors anddisplays. However, as discussed elsewhere, the system is designed toallow incorporation of made up components into partially printed objectsin the production line.

[0043] Flat Panel TV

[0044] A flat panel TV of 53 cm diagonal size is generally the largestobject that can be printed in the typical system. Of course to printwider objects, wider printheads may be utilized. For longer objects,more memory is required and for thicker objects the voxel height maybeincreased or more layers printed by providing more layer groups. Whilstthe printheads have the ability to vary the droplet size slightly,generally if a larger voxel size were required, different printheadswould be required. Of course increased voxel size results in a higher‘roughness’ of the finished product. However, depending on the product,this may be commercially acceptable.

[0045] A typical 53 cm flat panel TV has dimension of 450 mm×290 mm×10mm (H×W×D). Using hexagonal voxels 10 microns high and with a sidelength of 6 microns, a total of about 1395 billion voxels are requiredto define each product. This requires approximately 1395 Gbytes of data,if we assume that eight different materials are used in the product.

[0046] At a substrate speed of 208 mm per second a typical productionline can produce approximately 0.37 products per second (²⁰⁸/450=0.46),31890 products per day or 12 million products per year, assuming thesystem runs continuously.

[0047] The complexity that may be defined by over 1 terabyte of data ismuch greater than required by a typical flat panel TV and the amount offunctionality that can be built-in could be very great. There are veryfew discrete objects that would need to be incorporated into thepart-printed product.

[0048] From the foregoing it is apparent that the invention thus hasmany embodiments and accordingly has many broad forms.

[0049] In a first broad form the invention provides a three dimensionalobject creation system that prints objects layer by layer, the systemprinting at least part of each of multiple layers simultaneously.

[0050] In a second broad form the invention provides a three dimensionalobject creation system that prints objects layer by layer, the systemprinting at least part of each of multiple layers simultaneously,

[0051] wherein each layer is defined by a plurality of voxels arrangedin a regular array and wherein the voxels of each layer are printed soas to be offset by half a voxel relative to the voxels of adjacentlayers in a first direction, a second direction perpendicular to thefirst direct ion or both the first and second directions.

[0052] In a third broad form the invention provides a three dimensionalobject creation system that prints objects layer by layer, the systemincluding a plurality of printheads, the system printing at least partof each of multiple layers simultaneously,

[0053] wherein the printheads are configured to enable printing of atleast two different materials in at least one layer.

[0054] In a fourth broad form the invention provides a three dimensionalobject creation system that prints objects layer by layer, the systemincluding a plurality of printheads, the system printing at least partof each of multiple layers simultaneously,

[0055] wherein the printheads are configured such that at least one ofthe layers may be printed with a first set of materials and at least oneother of the layers may be printed with a second set of materials, andwherein the first and second sets are not the same.

[0056] Preferably more than 100 layers are printed simultaneously andmore preferably about 1000 layers are printed simultaneously.

[0057] Preferably pluralities of objects are simultaneously printed.

[0058] When completed, the objects may have substantially identicaldesigns.

[0059] Preferably each of the layers that are at least partially printedsimultaneously is for at least one different object.

[0060] Each printhead may print part or all of a predetermined layer.

[0061] Multiple layers of the same material may be printed

[0062] Multiple materials may be incorporated in each layer.

[0063] Preferably the printheads are inkjet printheads and morepreferably the printheads are fixed inkjet printheads able tosimultaneously print the width of the objects.

[0064] Droplets of material printed may be printed in a hexagonalclose-pack configuration or a face centered cubic configuration.

[0065] In a fifth broad form the invention provides a three dimensionalobject creation system that prints objects layer by layer, the systemincluding a plurality of printheads, the system printing at least partof each of multiple layers simultaneously,

[0066] the system configured to enable at least one first printhead thatis initially configured to print at least part of a first layer to bedynamically reconfigured to print at least part of a second layer.

[0067] Preferably the at least one first printhead is dynamicallyreconfigured if at least one of the at least one printhead initiallyconfigured to print the second layer fails.

[0068] Preferably if a printhead initially configured to print thesecond layer fails whilst printing the second layer, the at least onefirst printhead is reconfigured to complete the printing of at leastpart of said second layer.

[0069] In a sixth broad form the invention provides a three dimensionalobject creation system that prints objects layer by layer, the systemincluding a plurality of printheads, the system printing at least partof each of multiple layers simultaneously,

[0070] the system configured to enable at least one first printhead thatis initially configured to print at least part of a first layer to bedynamically reconfigured to print at least part of a second layer, and

[0071] wherein if at least one printhead initially configured to printthe second layer fails whilst printing said second layer, said at leastone first printhead is dynamically reconfigured to complete the printingof at least part of said second layer.

[0072] Preferably the reconfiguration is made with no loss of printedproduct.

[0073] Preferably the system includes a fault detection system thatautomatically detects faults in said system and reconfigures said atleast one first printhead in the event of a failure.

[0074] In a seventh broad form the invention provides a threedimensional object creation system that prints objects layer by layer,the system including a plurality of printheads, the system printing atleast part of each of multiple layers simultaneously,

[0075] the system including semiconductor memory and

[0076] wherein data defining at least one layer is stored in thesemiconductor memory.

[0077] Preferably the data defining all of the layers is stored in thesemiconductor memory.

[0078] Preferably each printhead includes at least some of thesemiconductor memory and more preferably the semiconductor memory ofeach printhead stores data relating to at least the part of the layerprinted by the printhead.

[0079] Preferably the semiconductor memory of each printhead stores datarelating to at least part of at least another layer and more preferablythe semiconductor memory of each printhead stores data relating to atleast part of the previous layer compared to the layer currently beingprinted by the respective printhead.

[0080] The system may include more than 10 Gbytes of semiconductormemory.

[0081] In a eighth broad form the invention provides a system thatexecutes a process, the system including a plurality of subsystems, eachof which performs a stage of the process,

[0082] each of the subsystems configured to perform one of a firstsubset of N₁ of the stages, where N is greater than 1, and to change thestage of the subset being performed on receipt of a change instruction;

[0083] wherein, in the event that one of the subsystems fails, at leastone of the remaining subsystems synchronously changes to performing therespective stage of the failed subsystem without requiring transfer ofdata relating the respective stage to the said at least one remainingsubsystems, and

[0084] when a subsystem changes to performing a different stage, thesystem reconfigures the subsystem to be capable of performing a secondsubset N₂ of the stages where N_(1 and N) ₂ have the same number ofstages.

[0085] The system may be a pipelined system in which each stage isdependent on the successful completion of all previous stages.

[0086] Preferably another subsystem is instructed to perform the stagepreviously carried out by the first subsystem.

[0087] The reconfiguration may occur by way of replacement of acomponent or, in preferred forms, by way of data transfer.

[0088] Preferably each stage is defined by a data set and each subsystemstores a plurality of data sets. When performing a stage the subsystemaccesses the corresponding data set. To change the stage beingperformed, the subsystem merely changes the data set being accessed.Preferably when a subsystem changes the stage being performed, the dataset relating to the stage previously being performed is replaced by datarelating to a stage not already in that subsystem's memory.

[0089] In preferred systems, when a subsystem fails, all subsequentsubsystems in the process change the stage being performed and, whenreconfiguration involves a transfer of data, preferably this occurs as apipelined data transfer.

[0090] In a ninth broad form the invention provides a printing systemincluding a least two printheads, wherein a first printhead is activelymaintained at a first temperature and a second printhead is activelymaintained at a second temperature.

[0091] Preferably the system is a three dimensional object creationsystem that prints objects layer by layer, the system including aplurality of printheads, the system printing at least part of each ofmultiple layers simultaneously.

[0092] Preferably the first printheads is configured to eject a metaland the first temperature is above the melting point of the metal.

[0093] In a tenth broad form the invention provides a printing systemincluding a least two printheads, a first one of the printheads printinga first material and a second one of the printheads printing a secondmaterial, the first material being cured by a first method and thesecond material being cured by a second method and wherein the first andsecond methods are different.

[0094] The first and second methods may include at least one methodselected from a group including: evaporative drying; freezing ofmaterial ejected when molten; ultra violet curing; addition of a curingagent.

[0095] The first and second methods may include printing of a curingagent simultaneously or sequentially with the respective material.

[0096] The first and second methods may include printing of a curingagent selected from a group including: a catalyst; a polymerizationinitiator; a compound that reacts with the respective material.

[0097] The system may be a three dimensional object creation system thatprints objects layer by layer, the system printing at least part of eachof multiple layers simultaneously.

[0098] In a eleventh broad form the invention provides a printing systemincluding

[0099] at least one printhead for printing material to create a printedproduct, and

[0100] an object incorporation device that incorporates inorganicsemiconductors into the product being printed whilst the at least oneprinthead prints the product.

[0101] The inorganic semiconductor may be an integrated circuit.

[0102] The inorganic semiconductor may comprises silicon.

[0103] The inorganic semiconductor may comprise a Group III-Vsemiconductor.

[0104] The inorganic semiconductor may comprises a discrete device.

[0105] The inorganic semiconductor may be selected from a groupincluding: transistor; light-emitting diode; laser diode; diode orsilicon controlled rectifiers (SCR).

[0106] The system may be a three dimensional object creation system andmay be a three dimensional object creation system that prints objectslayer by layer, the system printing at least part of each of multiplelayers simultaneously.

[0107] In a twelfth broad form the invention provides a system thatprints three dimensional products, the system including

[0108] at least one object incorporation device that incorporatesnon-printed objects into partially completed product, the non-printedobjects not being printed by the system.

[0109] The system may include at least one printhead for printingmaterial to create a printed product and operate so that non-printedobjects are incorporated into partially completed product whilst the atleast one printhead prints the product.

[0110] Preferably the non-printed objects are incorporated intopartially completed product without stopping the printing process.

[0111] Preferably the non-printed objects are incorporated into thepartially completed product at a predetermined position and/or apredetermined orientation on or in the product.

[0112] The system may print electrical connectors to electricallyconnect the non-printed objects to other parts of the product.

[0113] The system may print at least part of each of multiple layerssimultaneously. More preferably the system simultaneously prints objectslayer by layer.

[0114] In a thirteenth broad form the invention provides a system thatprints three dimensional products, the system including

[0115] an object incorporation device that inserts non-printed objectsinto a cavity created during the printing process, the objectincorporation device incorporating the non-printed object into thecavity during the printing of the respective printed object.

[0116] Each cavity may be created with substantially the same height asthe non-printed object to be inserted into the respective cavity.

[0117] Each cavity may be sized so that after insertion of the object,the top of the non-printed object is substantially flush with thesurrounding material of the partially completed product.

[0118] Each cavity may be shaped to maintain at least one of theposition and orientation of the non-printed object and preferably both.

[0119] The shape of each cavity may substantially match the shape of thenon-printed object.

[0120] The system may print at least part of each of multiple layerssimultaneously. More preferably the system simultaneously prints objectslayer by layer.

[0121] In a fourteenth broad form the invention provides a system thatprints three dimensional products, the system including

[0122] at least one printhead that prints electrical connections to atleast one object incorporated in the products.

[0123] Preferably the at least one object does not include a substrate.

[0124] A drop on demand printing subsystem preferably prints theelectrical connections.

[0125] The electrical connections are preferably printed with moltenmetal.

[0126] The system may print at least part of each of multiple layerssimultaneously. More preferably the system simultaneously printsproducts layer by layer.

[0127] It will be appreciated that the features of the various broadforms of the invention may combined together in any combination and arenot limited to any one specific broad form.

BRIEF DESCRIPTION OF DRAWINGS

[0128]FIG. 1 shows a schematic side view of a production line accordingto a first embodiment of the invention.

[0129]FIG. 2 shows a schematic side view of a production line accordingto a second embodiment of the invention.

[0130]FIG. 3 shows another schematic side view of the production line ofFIG. 2.

[0131]FIG. 4 shows a schematic side view of the production lineaccording to a third embodiment of the invention.

[0132]FIG. 5 shows a schematic side view of a production line accordingto a fourth embodiment of the invention.

[0133]FIG. 6 shows a schematic side view of a production line includingan object insertion device.

[0134]FIG. 7 is a plan view showing a number of voxels of the preferredembodiments.

[0135]FIG. 8 shows a side view of the arrangement of layers of voxelsproduced by preferred embodiments.

[0136]FIGS. 9a, b and c show plan views of an odd layer of voxels, aneven layer of voxels and an odd and even layer of voxels.

[0137]FIG. 10 is a diagram showing how each layer group stores datarelating to multiple layers of material in an initial printingconfiguration.

[0138]FIG. 11 is a diagram showing the situation when a first failure ofa layer group has just occurred.

[0139]FIG. 12 is a diagram showing the logical arrangement of layergroups after a first failure of a layer group when the layer groups havebeen remapped.

[0140]FIG. 13 shows the transfer of data after remapping of layergroups.

[0141]FIG. 14 is a diagram showing the situation when a second layergroup fails.

[0142]FIG. 14 is a diagram showing remapping of layer groups after thesecond failure but before all data has been transferred.

[0143]FIG. 16 is a diagram showing the situation when a third failureoccurs before the data transfer relating to the second failure hascompleted.

[0144]FIG. 17 is a diagram showing the next actions to accommodate thesecond and third failures.

[0145]FIG. 18 shows the next stage in the fault recovery process.

DETAILED DESCRIPTION OF PREFERRED AND OTHER EMBODIMENTS

[0146] Basic Concept

[0147]FIG. 1 schematically shows a simplified production line 100 havingmany substrate width printheads 102. The printheads 102 print materialsonto a moving substrate 104, that is preferably moved at a substantiallyconstant speed in a flat plane, as indicated by arrow 106. Theprintheads 102 extend across the width of the substrate 104perpendicular to the direction of travel of the substrate and are,preferably, spaced along the substrate 104 with substantially constantseparations. However, as will be explained later, constant separation ofthe printheads is not critical.

[0148] The printheads 102 print one layer of an object onto thepreviously printed layer. Thus the printhead 112 prints the first layer110, the second printhead 108 prints a second layer 114 onto the firstlayer 110 and the N^(th) printhead 116 prints an N^(th) layer 118 ontothe (n−1)^(th) layer 119. For clarity only one printhead is shown foreach layer but in practice there will be multiple printheads for eachlayer.

[0149] The layers are of a constant thickness and the printheads arecontrolled so that, in plan view, layers are printed on top of eachother.

[0150] The distance from each of the printheads to the surface uponwhich they print is also preferably the same for all printheads. Thusthe distance 122 from the first printhead 112 to the substrate 104 ispreferably the same as the distance 124 from the seventh printhead 126to the sixth layer 128. This may be achieved by sequentially raising theprinthead(s) for each layer by the voxel height. In this situation,droplets ejected by printheads for different layers at exactly the sametime will arrive at their destinations at the same time.

[0151] Voids

[0152] A product may be produced with voids and/or cavities. These voidsmay be utilized for location of separately created objects that areinserted into the cavities during production. The cavities may also beprovided as fluid passageways or for other purposes and remain ‘empty’of printed or inserted materials in the finished product.

[0153] Cavities that have substantially vertical walls and a roof canonly have the roof printed where there exists solid material in thecavity. Where an object is inserted, obviously the object provides thesolid surface onto which roof material may be printed. Where the cavityis to be ‘empty’ in the finished product, it is necessary to provide asacrificial material, such as wax, to provide a solid surface on whichthe roof material may be printed. The sacrificial material is thenremoved by further processing after the roof has been formed.

[0154] It will be appreciated that many cavity shapes do not require asacrificial material and the roof may be closed up gradually one layerat a time. Examples of such shapes include ovals and circles, polygonshaving an odd number of sides, and other shapes that do not have ahorizontal roof portion significantly greater than the voxel size.

[0155]FIG. 8 shows a product that has had a number of different cavitiesor voids formed in various layers. A triangular cavity 830 has beenformed that spans 5 layers. As can be seen, printing successive layerswith a smaller opening may close the cavity. The cavity 830 may extendas a passageway through the product and may extend vertically and/orlongitudinally, not just transversely. FIG. 8 also shows cavities 832,834 and 836 that are formed by not printing in a single layer. Cavity836 is shown partially completed and, in cross section has a diamondshape. When the fifth layer is completed, the cavity will be closed.

[0156] It will be appreciated that the drawing is not to scale and inpractice cavities may extend for 10's of voxels in either the transverseor longitudinal direction and may also extend for 10's of layers.

[0157] Multiple Materials

[0158] Whilst a system that only prints one material is within the scopeof the invention, to produce functional products made of many differentmaterials, the ability to print several different materials on a layeris required. In preferred embodiments this is achieved by providingmultiple printheads for each layer, with at least one printhead printinga different material compared to the other printheads provided for thatlayer.

[0159] Referring to FIG. 2 there is schematically shown a digitaladditive manufacturing system 200 for simultaneously creating multiplemulti-material products, one layer at a time. For clarity somecomponents are omitted.

[0160] The products printed simultaneously may all be of an identicaldesign or may be of different designs, depending upon data supplied tothe printheads. Different designs of products may be printed side byside and/or end on end or on top of each other. Products may be printedon top of each other using sacrificial material(s) as separatinglayer(s).

[0161] The system 200 includes a conveyor or substrate 202 that iscaused to move at a substantially constant velocity as indicated by anarrow 204. The substrate 202 may be directly driven or may be located ona conveyor system, not shown. The substrate 202 preferably moves in aflat plane. Movement along a non-flat plane is also possible. Acontinuous substrate is preferred as this ensures a consistent velocitypast all the printheads. However because discrete objects are created, aseries of discrete carriers could be conveyed past the printheads.

[0162] Located above the substrate 202 and spaced apart form each otherare a series of “layer groups” 206 of printing devices. Each layer group206 includes m printheads 208, which extends transversely across thesubstrate 202 perpendicular to the direction of travel of the substrate.There may be more than one printhead in each layer group; for a typicalsystem there will be an average of around eight printheads in each layergroup. For clarity the drawings only show four printheads in each layergroup. There is no theoretical limit to the number of printheads in eachlayer group. In the embodiment of FIG. 2 the layer groups are identicalto each other.

[0163] The materials printed by the printheads may include differentpolymers, different colored polymers, metals, sacrificial materials suchas wax, various evaporative drying materials and various two partcompounds. A suitable metal that may be used is indium, which has amelting point of 156° C. Alloys of Indium and Gallium may be used, withmelting points below 156° C. It will be appreciated that other metals ormetal alloys may be used. The ability to print metal enables highconductivity electrical connections to be printed. Polymers havingmelting points in the range of about 120° C. to 180° C. are preferred,but other polymers may be used. Sacrificial waxes having a melting pointof above 80° C. are preferred. Other compounds may be printed.

[0164] The layer groups 206 are spaced apart along the longitudinaldirection in which the substrate 202 moves. The spacing of the layergroups 206 from each other is preferably substantially constant but thisis not essential. The layer groups 206 are spaced vertically from thesubstrate 202 and this vertical separation preferably increases stepwisewith each layer group in the longitudinal direction by β for each layergroup. Thus, the m^(th) layer group will preferably be β(m−1) furtheraway from the substrate 202 than the first layer group, where β is theincrease in vertical separation per layer group. The value of β ispreferably at least the voxel height α, approximately 10 microns. Thestep value may be greater than the voxel height α but in mostembodiments cannot be less than the voxel height. A value greater than αmerely results in the printhead to printing surface increasing. A valueless than α may result in products contacting the printheads unless theinitial vertical spacing is sufficiently large. However, in practice theprinthead to surface distance is significantly less than the finishedproduct height. So β needs to be the same or greater that the voxelheight α. The printheads of each layer group are preferably the samedistance from the substrate so that they may be synchronized to a singleclock and so preferably β is equal to α. Variations in vertical positionof individual printheads in each layer group may be compensated for byadjusting when each of the printheads operate.

[0165] As the substrate 202 moves in the direction of arrow 204, all ofthe layer groups operate simultaneously, so that each layer group laysdown a single layer of material or materials of the products beingcreated. By simultaneously we mean the printheads operate atsubstantially the same time; we do not mean that the printheads ejectmaterial at exactly the same time. In fact, because the printheads of asingle layer group are spaced along the path of travel, by necessitythey must eject material at different times.

[0166] The first layer group 210 prints material directly onto thesubstrate 202 to form a first layer 211. Thus as the substrate passesunder the second layer group it will already have material printed bythe first layer group. Thus the second layer group 212 prints a secondlayer of the object onto that first layer. In normal operation eachlayer group prints a layer onto the layer printed by the previous layergroup so that the n^(th) layer group 214 prints an n^(th) layer 216 ofthe object.

[0167] If the spacing of the layer groups along the substrate isconstant and a single type of object is being produced, the front edgeof all the objects being simultaneously created by the production linewill pass under the first printhead of each layer group at the sametime. If the distances between the first printhead of each layer groupand the surface upon which material ejected by that printhead aresubstantially identical, then the time that material spends travelingfrom the printhead to the deposition surface is also the same betweenthe layer groups. Thus, the layer groups may be synchronized to run offa single clock without, in normal use, the need for delays in the clockcycles between layer groups. As will be explained later, the system isdesigned to operate with variations with longitudinal spacing betweenadjacent operating layer groups and constant longitudinal spacing orvertical rise is only preferred and is not always critical.

[0168] To maintain a substantially constant step height between layergroups, the printheads of the layer groups may be mounted directly orindirectly on two longitudinally extending support beams. Assuming thebeams are substantially straight, for a production line of 1000 layergroups, raising the downstream end of the beams 1 cm compared to theupstream ends will result in a step height for each layer group of 10micron, assuming there is a constant spacing between the layer groupsand the layer groups are all the same size in the longitudinaldirection. Where there are multiple printheads in a layer group theprintheads may be mounted individually to the beams or may be mounted ona common carrier with the carrier mounted on the beams. Mounting theprintheads of each layer group on a common carrier allows the printheadsto be more easily located substantially in a single plane. In use theplane is also preferably substantially parallel to the substrate. Thisallows the printheads of a layer group to have a common printhead toprinting surface distance where the substrate moves on a plane. The useof a common carrier also allows the printheads of a layer group to beassembled on the carrier away from the production line with thelongitudinal spacing between printheads accurately controlled. Locationof the printheads on the beams then merely requires accurate location ofthe carrier. Replacement of a failed layer group is also easier.

[0169] The multiple printheads of each layer group are for printing asingle layer but they are spaced apart from each other. Referring toFIG. 2, material 218 printed by the m^(th) printhead 208 m may need tobe printed adjacent to material 220 printed by the first printhead 208 aof a layer group. This is achieved by delaying printing of voxels by them^(th) printhead 208 m compared to those printed by the first printhead208 a. This time delay corresponds to the time the substrate 202 takesto move from the first printhead 208 a to the m^(th) printhead 208 m,i.e. the separation of the printheads divided by the speed of thesubstrate 202. Since both the substrate speed and the longitudinalseparation of printheads in a layer group may vary, the time delay isnot necessarily constant. This may be due to temperature variations,variations in location of printheads and other factors. Accordingly thesystem may include sensors that feed data such as temperature, substratespeed or printhead separation into the timing circuits.

[0170] Print Temperatures

[0171] Each of the different materials used may require differentprinting and/or post printing processing temperatures compared to thetemperatures required for the other materials. The actual printingtemperatures and post printing processing temperatures depend on thematerials used and so it is conceivable that a multi material productionline could run at one temperature, albeit unlikely. It also follows thatnot only must the materials used must be compatible with the othermaterials during printing, processing and in the finished product, butthat the printing and processing temperatures must be generallycompatible.

[0172]FIG. 3 shows the production line of FIG. 2 but indicating printtemperatures.

[0173] The printheads of each layer group 206 may print severaldifferent materials, typically materials that are heated above theirmelting points. Accordingly, one printhead may print indium metal at atemperature of 180° C. Sacrificial wax having a melting point of about80° C. or lower may be printed by another printhead to enable theformation of voids. If both indium and wax are printed, the evaporativetemperature of the wax will need to be below the melting point of indium(156° C.). If the evaporation temperature of the wax were above 156° C.,when the product is heated to evaporate the wax, the indium metal wouldmelt. Accordingly, a wax with an evaporative temperature below 156° C.(or the lowest melting point of all other materials used) must be used.The wax also cannot be heated to 180° C. for printing, as at thattemperature it is a vapor. Accordingly, the printhead printing the waxwill need to be at a temperature of about 80° C. whilst the indiumprinthead will need to be at about 180° C. Similar considerations applywhen printing materials that are printed in solution and the solventevaporates to ‘cure” the material. These materials may well be printedat room temperature.

[0174]FIG. 3 shows the first printhead of each layer group, such asprinthead 208 a, prints a first material M₁ at a temperature T₁ Thesecond printhead of each group, such as printhead 208 b prints a secondmaterial M₂ at a temperature T₂, etc. The m^(th) printhead of eachgroup, such as printhead 208 m prints material M_(m) at temperatureT_(m). Some of the values of T₁ to T_(m) may be the same.

[0175] Whilst reference is made to the melting point of other materials,it will be appreciated that some materials, either before or afterprinting or curing, may undergo undesirable temporary or permanentchanges if raised about certain temperatures. If so, the system needs tobe configured to avoid subjecting those materials to temperatures abovethe relevant thresholds.

[0176] The temperatures of the materials printed and the temperature ofthe exposed layer needs to be maintained within ranges. The concept ofthe invention hinges on voxels bonding to adjacent voxels to form aproduct of acceptable strength and durability. Thus, for instance, adroplet of indium metal may be printed onto a voxel of indium metal or aplastics material. The droplet of indium will need to be heated to atemperature sufficiently above its melting point so that it may meltpart of the indium upon which it lands to forming a good mechanical andelectrical bond. However, the indium should not be so hot that it meltstoo much of the material that it contacts or otherwise irreversiblychanges the material that it contacts. It will be appreciated that therequirements for good bonding and avoiding damage to previously printedmaterial can be accommodated by adjusting the temperature of materialbeing printed and the temperature of the material that has been printed,as well as by appropriate selection of materials.

[0177] Curing Methods

[0178] Different materials printed by the system may require a number ofdifferent curing techniques. Two or more materials usually share adrying/curing technique. FIG. 4 also schematically shows a number ofdifferent curing techniques.

[0179] Curing requirements include simple cooling to cause a material tosolidify, evaporative drying, precipitation reactions, catalyticreactions and curing using electromagnetic radiation, such as ultraviolet light.

[0180] The materials of each layer need to be cured to a sufficientdegree to be dimensionally stable before the materials of the next layerare deposited. Preferably the materials are fully cured before the nextlayer is deposited but need not be. For example a material printed as ahot melt may have cooled to be sufficiently ‘solid’ to allow the nextlayer to be printed whilst not being fully solidified. Examples includematerials that do not have a specific melting point but solidify over atemperature range.

[0181] Curing may occur after all materials in a layer have been printedor may occur at different stages. Thus, in some embodiments, each layergroup may include one or more mechanisms for effecting curing of thematerials printed that are located between printheads of each group.

[0182]FIG. 4 shows two layer groups of n layer groups of a system 400.The first layer group 402 has four printheads 402 a, b, c & d requiringtwo different curing methods. The second layer group 404 has mprintheads printing m materials requiring j different curing methods.Disposed within the printheads are curing mechanisms for carrying outappropriate curing methods. The printheads are preferably arranged sothat materials requiring the same curing method are grouped togetherupstream of a single corresponding curing mechanism.

[0183] The materials 403 a, 403 b of printheads 402 a and 402 b requirea first curing method and are located upstream of curing mechanism 406,which carries out curing of materials 1 and 2 as they pass underneath.The materials 403 c and 403 d printed by printheads 402 c and 402 dshare a second curing method and so are preferably grouped togetherupstream of curing mechanism 408. Thus the materials printed byprintheads 3 and 4 may be cured as they pass under curing mechanism 408.

[0184] Similarly, the second layer group 404 has materials that requirethree different curing methods. Printheads 404 a and 404 b printmaterials 405 a and 405 b that require curing by the first curing methodand are located upstream of curing mechanism 410. The third and fourthprintheads 404 c and 404 d print third and fourth materials 405 c and405 d that are cured by curing mechanism 412. Finally, the fifth tom^(th) printheads print materials that require a j^(th) curing method,which is effected by the curing mechanism 414.

[0185] By grouping the printheads of materials that share common curingtechniques together, only a single curing mechanism for each curingmethod is required in each layer group. Whilst this is preferred, thereis nothing to prevent an arrangement where one curing method is carriedout by more than one curing mechanism in each layer.

[0186] It will be appreciated that curing methods may conflict and sothe order of printing within each layer group will require considerationto ensure a curing method does not adversely affect other materialsalready printed, whether cured or uncured.

[0187] In some circumstances all curing devices may be located betweenlayer groups.

[0188] Examples of curing methods include, but are not limited to, thefollowing:

[0189] Evaporative drying.

[0190] Freezing of ejected material.

[0191] Ultra violet initiated curing using U.V. lamps.

[0192] Printing of reagents.

[0193] Printing of catalysts or polymerization initiators.

[0194] Evaporative Drying.

[0195] Evaporative drying may be assisted by passing a hot or dry(solvent depleted) gas over the material, applying a vacuum or low gaspressure to the material or by heating, such as by infrared radiation orcombinations of these. It will be appreciated that by ‘dry’ gas we meangas that has a relatively low partial vapor pressure of the relativesolvent, whether that solvent is water, alcohol, another organicsolvent, an inorganic solvent, etc.

[0196] Freezing of Ejected Material.

[0197] Freezing of ejected material that has been heated above itsmelting point is applicable to metals, polymers and waxes. Cooling mayrely on conduction and/or radiation of heat only or may be enhanced byblowing of cold gas over the layer or any other method of forced coolingto speed heat removal. Since the preferred production line has of theorder of 1000 layer groups, conduction and radiation alone will notusually allow sufficient heat loss and so forced cooling will berequired in most situations. As each layer needs to be cooled, gas(es)will normally be caused to move transversely across the objects. Coolinggases may be introduced on one side of the system and caused to flowacross the object to the other side. Alternatively gas may be introducedabove the objects and caused to flow to both sides of the object. Itwill be appreciated that these are examples and other systems for gasflow may be utilized. It will be understood that ‘cold’ is relative andthe gases used may be at or above ambient temperature.

[0198] Where gas is passed over the layer, either for evaporative dryingor for freezing, it will be appreciated that the gas will need to becompatible with the material or materials being cured. Where metals areprinted, the metal droplets will, generally, need to fuse with adjacentmetal droplets, either in the same layer or in adjacent layers. As suchan inert gas, such as nitrogen, will be needed for cooling so as toavoid oxidation.

[0199] In most circumstances material ejected as hot melt needs to becooled not only below its freezing temperature but also to the freezingtemperature of all the materials printed. Potentially any of thematerials may be printed next to or on top of any other material. As anexample, indium metal may be printed in part of one layer and the nextlayer may have sacrificial wax printed onto the indium metal of theearlier layer. Whilst the indium could be cooled to about 150° C. to befrozen, this would be too high for a sacrificial wax with a meltingpoint of about 80° C. Thus, the indium would need to be cooled to below80° C. in this case before reaching the next layer group. In addition,sacrificial wax may be printed in the same layer and adjacent to indiummetal. In this case the indium metal would need to be cooled below themelting point of the wax before reaching the wax printhead of the samelayer group. It will be appreciated that a first voxel of material maybe heated by a nearby second voxel even though the two voxels are not inphysical contact with each other. Whilst wax has been used as an exampleof a material having a low melting point, it will be appreciated thatthe above discussion is applicable to all materials.

[0200] The effect of high temperatures is not limited to possiblemelting. High temperatures may also affect materials that are cured byother methods, such as evaporation, catalytic reactions orpolymerization reactions.

[0201] It follows from the above discussion that, in most situations,materials that require a high processing temperature, whether due tobeing printed as a hot melt or due to post printing processing, willneed to be printed, processed and cooled to an acceptable temperaturebefore printing of potentially affected materials in the same layer, notjust in the next layer.

[0202] Ultra Violet Initiated Curing Using U.V. Lamps.

[0203] Ultra violet curing may be used with U.V. cured polymers. Toachieve rapid curing high intensity U.V. lamps may be used. To avoidoverheating forced cooling by passing cooled gas may also be required.

[0204] Printing of Reagents and Catalysts or Polymerization Initiators.

[0205] Reagent printing includes printing of two part polymers ormixtures in which a precipitation reaction occurs. This may requirespecial printheads to print the two compounds simultaneously or the useof two, preferably adjacent, printheads, that each print one of thecompounds. Similarly, use of catalysts or polymerization initiatorsrequires printing of the material and a catalyst or polymerizationinitiator. Thus, again, special ‘dual’ printheads or two printheads maybe required for each such material.

[0206] Where a solid material is produced by use of catalysts,polymerization initiators, two part polymers, precipitation reactions orother mechanisms that require two separate components to be printedseparately, the two components may be printed to the same location ormay be printed to adjacent locations with mixing occurring throughcontact of adjacent voxels. It will be appreciated that with two partcompounds, one of the compounds, such as a catalyst, may be required inmuch smaller qualities than the other compound.

[0207] It will appreciated that there may be cases where more than twoprecursors are printed to form one ‘finished’ material.

[0208] Printing of two or more different materials to the same locationresults in more homogeneous voxels of the end material, but requiresgreater accuracy than printing to adjacent locations.

[0209] Reduced Capability

[0210] Whilst a production line having identical layer groups providesmaximum flexibility, for many products this is not needed. For example,many products have a plastic shell. Thus, for example, the first fewhundred layers may only require a single material forming the base ofthe shell. Thus the production line may dispense with printheads thatare effectively redundant, so reducing complexity, size and overall costof the production line. Accordingly some of layer groups may have areduced number of printheads.

[0211]FIG. 5 shows the first nine layer groups 506 to 522 in a system500 having n layer groups.

[0212] The first four layer groups, 506 to 512, only have one printheadwhilst the fifth, sixth and seventh layer groups 514, 516 & 518 have twoprintheads each. The printheads of each pair print a different materialto that printed by the other printhead of the pair. The eighth layergroup 520 has four printheads, printing four different materials whilstthe ninth layer group 522 has two printheads, again printing twodifferent materials. It will be appreciated that the number ofprintheads in other layer groups does not necessarily dictate the numberof printheads in a layer group.

[0213] The materials printed by each multi-material capable layer groupmay be the same or different from each other. Thus, for example, thefifth and sixth layer groups, 514 & 516, have printheads 514 a and 516 athat print material M₁ and printheads 514 b and 516 b that print a thirdmaterial M₃.

[0214] The seventh layer group 518 has a printhead 518 a that prints asecond material M₂ and a printhead 518 b that prints an n^(th) materialM_(n). Printheads 520 a, b, c & d of layer group 520 print materials M₁,M₂, M₃ and M_(n), respectively.

[0215] Whilst FIG. 5 shows layer groups at the start of the productionline having a reduced number of printheads compared to the maximumnumber of materials printed, it will be appreciated that any layer groupin the production line may be limited to printing less materialscompared to the maximum number of materials that are able to be printedby the system.

[0216] Insertion of Objects

[0217] At this stage, because the present minimum resolution is about 10micron, it is not possible for the system to print all requiredcomponents of a product. Some components may require finer resolution,such as high-speed semiconductors.

[0218]FIG. 6 schematically shows a production line 600 including a robot602 for insertion of objects into the products being printed. Forclarity the vertical and horizontal scales are exaggerated.

[0219] The robot 602 has a supply 606 of objects 604 to be inserted. Therobot 602 takes one object at a time and accelerates the object 604horizontally to travel at the same speed as the conveyor. The object 604is then moved vertically to be inserted into a cavity 608 previouslyprinted in the product. The cavity 608 is a close fit for the object 604being inserted and alignment of the object with the cavity is preferablyachieved using vision systems. The cavity is preferably sized so thatthe top of the object does not protrude above the top layer of theobject.

[0220] Whilst the drawing shows a cavity five voxels high by nine voxelslong, this is not to scale. Typically, objects to be inserted havedimensions of the order of millimeters, not microns. A typical objectmay have a size of 5×5×1 mm (L×W×H) i.e. 5000×5000×1000 microns. Whilsta height of 1 mm may seem small, the clearance between the top layer ofthe product and the printheads is typically also only about 1 mm. Thus,an object placed on the top layer rather than in a cavity may not cleardownstream printheads. Additionally, if the object extends above the toplayer, this may cause unpredictable airflows and cause unintendeddisplacement of drops subsequently printed. By inserting, the objectinto a cavity having a depth at least as great as the object's height,the highest point of the object is flush or below with the top of theproduct and so does not cause any unexpected results.

[0221] Preferably the cavity is sized so that the object is securely andcorrectly located in the cavity. Placing the object in a cavity alsoreduces the risk that the object may be moved unintentionally, which mayoccur if it were placed on the top surface. The outline of the cavitypreferably matches the object. Thus, preferably, a rectangular objectwill be received in a rectangular cavity. However, it will beappreciated that this is not essential. The object may be received in acavity that holds the object in position but does not have a shape thatmatches the object's shape. For example, a rectangular object could belocated in a triangular cavity, so providing free space about theobject. The cavity may be shaped and configured to provide one or morechannels or passageways to other locations within the product or to theoutside of the product. Thus, for instance, a semiconductor chip may belocated in the product and provided with one or more cooling channels,ducts or passageways that extend to the outside of the finished product.

[0222] Key types of objects to be inserted typically include integratedcircuits such as main processors, memory etc. Whilst it is possible touse package chips it is better to use bare dies for cost, size andweight reasons. Preferably known good dies (KGD's) are used.Semiconductor that may be inserted include but are not limited totransistors; light-emitting diodes; laser diodes; diodes or SCR.

[0223] As mentioned previously, one of the materials that may be printedis indium. Another material that may be printed is an insulator, andaccordingly it is possible to print insulated electrical ‘wires’ 610,612 & 614 in the product. This may be carried out both before or afterinsertion of the device into the cavity. Whilst the drawing is not toscale, the electrical wires may have a thickness of 10 to 20 microns,i.e. one or two voxels. Wires may be placed in the order of 30 micronsfrom each other and so many millions of wires may be printed inrelatively small volumes.

[0224] Where electrically active devices are inserted, the devices arepreferably inserted with the bond pads 616 facing upwards as this makesthe forming of good quality electrical connections much easier. Withupward facing bond pads, electrical connections may be formed in thenext few layers to be printed. In contrast, bond pads on the bottom orsides of the object will rely on correct placement of the object andgood contact.

[0225] The device to be inserted may be cleaned by the insertion robotand the printing may occur in a nitrogen atmosphere, or a partial orhigh vacuum. The bond pads may be plated with indium metal such thatwhen indium is printed onto the bond pads the indium on the bond padmelts forming a good electrical connection.

[0226] Once the device has been inserted, downstream layer groups maythen print electrical connections. FIG. 6 schematically shows fourdownstream layers part-printed on the object and showing threeelectrical connections 610, 612 & 614 printed in upper layers to jointwo objects 604 a & 604 b together. It can also be seen in FIG. 6 thatearlier layers include metal voxels forming electrical wire 618.

[0227] The invention is not limited to insertion of electrical devices.Mechanical devices may also be inserted.

[0228] Typical System Characteristics

[0229] The following characteristics relate to the preferred embodimentsthat utilize MEMS inkjet type printheads as referenced in theaforementioned specifications.

[0230] Voxels

[0231] The building block of the printed object is a voxel. In thepreferred embodiment planar layers are printed that have the samedimensions and voxels all of the same dimensions. Most preferably thevoxel centers have a hexagonal close pack arrangement.

[0232] In the preferred embodiments the voxels 710 have a side length712 of 6 microns, as shown in FIG. 7. The height of the voxels isnominally 10 micron. This provides a resolution that is typically 10times higher than existing systems in each direction, giving a voxeldensity typically 1000 times greater than existing systems. Acorresponding nozzle of a printhead prints each voxel and so the nozzlesof the printheads have corresponding spacing. One or more in rows ofvoxels 710 are printed by each printhead, with each row extending acrossthe substrate, ads indicated by arrow 716. Rows are printed side by sidealong the substrate, as indicated by arrow 718. The nozzle pitch 720 is9 micron, whilst the row spacing 722 is 10.392 microns

[0233] Each drop of liquid material printed may be treated as a sphere,which in the typical system has a diameter of about 12 microns. When inposition and after becoming solid, each drop forms a voxel, with a shapeapproximating a hexagonal prism with a height of a, the layer height,which in a typical system is about 10 microns.

[0234] The voxels may be printed in a face centered cubic configurationor in a hexagonal close packed configuration. These configurations havea number of advantages, including increased resistance to crackpropagation, smaller voids between drops, and lower resistance ofprinted conductive lines. Other voxel configurations are possible, withcorresponding voxel shapes.

[0235]FIG. 8 shows a substrate 810 with a number of layers having beenprinted is shown. The voxels of even layers 811, 813, 815 and 818 areoffset longitudinally by half the voxel spacing relative to the voxelsof odd layers 810, 812, 814 and 816. This results in the voxels having ahexagonal arrangement in side view. The number of printheads per layerdoes not affect the voxel configuration and for clarity only oneprinthead per layer group is shown.

[0236] To achieve the longitudinal offsetting of the voxels 820, thespacing of the printheads 822 in the longitudinal direction ispreferably the same between all layer groups and is more preferably anintegral number of voxels plus half a voxel. This separation is notcritical and it is possible to achieve this half voxel longitudinaloffsetting of the printed layers by adjusting when each printhead ejectsink or by a combination of physical offsetting and timing adjustment.

[0237] The preferred printhead utilizes two rows of nozzles to print asingle “row” of voxels. The nozzles for odd drops or voxels are locatedin one row and the nozzles for even drops or voxels are located inanother, parallel, row. The two nozzle rows are spaced half a voxelapart transverse to the row direction and are staggered half a voxelparallel to the row direction so that when printed a “row” of odd andeven voxels is not a straight line but a zigzag line. FIG. 9a shows asingle “row” 901 shaded for clarity. If we assume the printed dropletsassume a hexagonal shape in plan view, continuous printing of rows canresult in total tiling of the surface with drops. It will be appreciatedthat other printhead configurations are possible. The main requirementis that, when printed, the droplets can form a substantially continuouslayer.

[0238]FIGS. 9a, b and c show how, in preferred embodiments, odd and evenlayers of materials are deposited relative to each other. For ease ofreference, a reference mark 900 is shown to indicate relative positions.Referring to FIG. 9a, the odd layers 902 are all printed with no“offset”. All even layers 904 are printed with a constant offset,relative to the odd layers 902. The even layers are offset by half avoxel in the transverse direction, as shown by numeral 906 in FIG. 9b.The even layers are also offset half a voxel in the longitudinaldirection, as shown by numeral 908 in FIG. 9b. The resulting relativepositioning of an odd and even layer is shown in FIG. 9c. This resultsin each voxel being offset half a voxel in both the x and y directions.Whilst it is preferred that offsetting occurs in both the longitudinaland transverse direction, it will be appreciated that the voxels may beoffset in only one of the longitudinal or transverse directions.

[0239] Transverse offsetting can be achieved by offsetting theprintheads. Thus printheads for odd layers can be offset half a voxeltransversely relative to printheads for even layers.

[0240] Whilst it is preferred that the physical offsetting of theprintheads in the longitudinal and vertical direction is constant,variations in both directions can be adjusted for by adjusting when theindividual printheads eject ink relative to the others.

[0241] Printhead and Layer Group Construction

[0242] A typical system is preferably capable of producing objectshaving up to eight different materials and, accordingly, will preferablyhave eight printheads per layer group.

[0243] Each printhead of a typical system has a printable width of 295mm, although this may be more or less, as desired. Each printheadincludes sixteen printhead chips arranged end on end, with an effectivelength of 18.4 mm. To increase printing speed each printhead preferablyprints two rows of material simultaneously, thus requiring two rows ofnozzles. In addition, two additional rows of nozzles are provided forredundancy. Accordingly, each printhead and printhead chip is providedwith four rows of nozzles.

[0244] Each printhead chip prints 2048 voxels per row and so eachprinthead chip has 8192 nozzles and each printhead has 131072 nozzles.

[0245] Where each layer group has eight separate printheads thisrequires 128 printhead chips per group and so there are a total of1,048,576 nozzles per group.

[0246] With a layer height of 10 microns, a typical system requires 1000layer groups to produce an object 1 cm high and so requires 8000printheads, 128000 printhead chips and provides 1,049 million nozzles.

[0247] Print Speed

[0248] The nozzle refill time of a typical printhead nozzle is about 100microseconds. With two rows of material printed simultaneously by eachprinthead, this provides a printed row rate of 20 kHz. At a row spacingof 10.392 micron in the longitudinal direction this allows a substratevelocity of 208 mm per second. Thus, for example, the system can producean object 30 cm long about every 1.5 seconds.

[0249] With a print width of 295 mm this provides a maximum print areaof 61 296 mm²/sec and a maximum print volume (at 10 micron voxel height)of 612963 mm³/sec per layer, assuming no voids. For a 1000 layer systemthis is a total of 0.613 liter/sec. It will be appreciated that in amultiple material object, most layers will be made of differentmaterials. Thus, whilst the maximum volume rate will be this value, eachprinthead will not be printing at the maximum rate.

[0250] Memory

[0251] In the preferred embodiments we have a system that may require upto about 98 Gbytes of data. Since we have all the layers of a definedproduct(s) being produced simultaneously, all of that data is beingaccessed effectively simultaneously. In addition, the data is being readrepetitively. Assuming a product size of about 450 mm longitudinally,each and every layer is printed about every 2½ seconds and so therelevant data needs to be accessed every 2½ seconds. For shorter layers,the data is read more frequently.

[0252] The quantity of data and the need to access the datasimultaneously and continuously means that, with present technologies,it is not practical to store the data in a central location and/or touse disk drives to store the data that is accessed by the printheads. Ifdisk drives were used they would be used continuously and be a majorrisk of failure. To provide disk redundancy would also result inunnecessary complexity. As solid state memory has no moving parts, itsfailure rate is much lower. Accordingly, in the preferred embodimentsthe data is stored in solid state memory and this solid state memory isdistributed across the layer groups of the system. Each layer groupstores data relating to the layer currently being printed by that layergroup in memory located on or in the layer group. Once the necessarydata has been downloaded to the layer groups, they do not need to accessan external source of data, such as a central data store. Byincorporating the memory in the layer group, and more preferably inprintheads or printhead chips, high speed access to the data for eachand every layer group is readily provided “internally”. In the typicalsystem each layer group normally prints one layer repeatedly and so, ata minimum, only needs to access the data for one layer at any one time.In preferred embodiments each layer group also stores data relating toother layers, for fault tolerance, as will be discussed later.

[0253] The memory used is preferably Dynamic Random access Memory(DRAM). Currently available DRAM provides sufficiently fast read accessto meet the requirements of the system. In the preferred embodimentsthis memory is located on each printhead.

[0254] In the preferred systems each printhead is constructed of sixteenprinthead chips and those printhead chips each have 4096 active nozzles.Each printhead chip is provided with 256 Mbits of DRAM to define therelevant portion of the layer to be printed, or 64 Kbits per nozzle. Ifwe allow 2 Kbits to define the layer and the specific material we haveapproximately 62 Kbits for voxel locations per nozzle. Thus we canspecify up to about 63,000 (62×1024) locations longitudinally. With alongitudinal size of each voxel of 10.392 micron this equates to amaximum product length of about 660 mm. This does not allow forredundancy or other overheads that may reduce the available memory andso the maximum number of locations.

[0255] Thus, a printhead having 16 printhead chips has 4096 Mbits ofDRAM and with 8 single material printheads per layer group, each layergroup has 32,768 Mbits of DRAM. A production line having 1000 layersgroups thus has 32,768,000 Mbits or 4096 Gbytes of DRAM. Whilst this isa significant amount, the cost is relatively low compared to theproductivity possible with the system.

[0256] It will be appreciated that the total amount of memory providedis dependant on the total number of different materials used and themaximum size of objects to be produced. Whilst the transverse length ofthe printheads limits the size of objects in the transverse dimension,there is no limit on the size of objects in the longitudinal direction.The maximum size is limited by the memory provided which is also themaximum amount of memory required. When defining a voxel in the product,the material in the voxel and the layer in which it occurs needs to bespecified. However, it is possible to dispense with this data at theprinthead level. In the typical system each printhead only prints onematerial in only one layer. If the printhead only stores data relatingto voxels that it prints, the data specifying the layer and material isredundant. Thus, potentially, the amount of data stored per printheadmay be reduced. However, as set out above, this saving is relativelynegligible.

[0257] Data Rate

[0258] Each printhead chip operates at 100 KHz, prints two rows ofvoxels each of 2048 nozzles and so requires a data rate of 39Mbits/second so (4096 nozzles at 100 KHz). This is well within thecapabilities of currently available DRAM. This results in data rates of625 Mbits/second for each printhead, 5000 Mbits/sec for each layer and5,000,000 Mbits/sec (or 625 Gbytes/sec) for the entire production line.It is thus quite impractical at present to have a central data store andto pipe the data to the individual printheads. It will be appreciatedthat if future developments allow sufficiently high data transfer ratesto be practicable, one or more centralized data store(s) may be used asthe source of print data, rather than relying on distributed memoryresiding on the printheads or printhead chips themselves.

[0259] A central data store defining the products(s) is required but thedata from that store only needs to be downloaded to the individual layergroups, printheads or printhead chips when the product(s) being producedchange, either totally or when modified. Whilst the system may requireof the order of 4096 Gbytes of memory in the layer groups, this transferdoes not need to be “instantaneous” as changes will be downloaded whenthe system is not operating.

[0260] Fault Tolerance

[0261] In a system with approximately 1000 layer groups, 8 printheadsper layer group, 16 printhead chips per printhead and 2048 nozzles perprinthead chip, there will be about 1 billion nozzles. As such, it isexpected that spontaneous failures will be a regular occurrence. It isnot practicable to stop the manufacturing process to replace failedprintheads, as this will require scrapping of all partially completedproducts on the conveyor. Thus, a 1000 layer manufacturing line may losethousands of products every time the system unexpectedly stops. Thenumber of products on the production line depends on product size,product spacing on the conveying system and the spacing of layer groups.Planned stoppages do not result in scrapping of product as each layergroup, commencing with the first, may be sequentially turned off to stopproducing products.

[0262] There are two primary levels of fault tolerance that aim toprevent unexpected stoppages. One is within the printhead itself and oneis between layer groups.

[0263] Printhead Fault Tolerance

[0264] Each printhead provides a level of fault tolerance. In thepreferred embodiments in which stationary printheads are used, theprinthead chips are provided with redundant nozzle arrays. If a nozzlefails, a corresponding nozzle in one of the redundant nozzle array(s)may take up its function. However, since the printheads are fixed, eachnozzle prints at the same transverse location and can only be replacedby one or more specific redundant nozzle(s). In a printhead with one setof redundant nozzles, each row location can only have one failure beforethe printhead becomes unable to correctly print material at alllocations. If a nozzle fails, the corresponding redundant nozzlereplaces it. If that ‘redundant’ nozzle then fails, it cannot bereplaced and so the entire printhead would be considered to have failed.Whilst the preferred embodiments only have one redundant nozzle for eachlocation, more than one set of redundant nozzles may be provided.

[0265] It will be appreciated that in a multi-material system eachprinthead does not necessarily print a full row. This depends on theproduct or products being printed. Thus many printheads will onlyutilize some of the printhead nozzles when producing products. Thestatus of unused nozzles is not relevant to the ability to correctlyprint the current product and so the printheads may be configured todetermine from the product data relating to the layer being printedwhich nozzles need to be tested both before printing and whilst printingis occurring.

[0266] For fault tolerance reasons, as discussed later, a printhead mayneed to keep an inventory of failed but unused nozzles, as these nozzlesmay be needed if the layer group needs to print another layer. Thus atinitialization, each printhead may test all nozzles independent ofproduct data. After determining if any nozzles have failed, thosenozzles may be mapped against the product data to determine if theprinthead should be mapped as failed or not. If a printhead isconsidered to have failed, then generally the entire layer group must beconsidered to have failed.

[0267] Layer Group Fault Response

[0268] The preferred system relies on each layer group carrying outtesting of itself and of the immediately upstream or downstream layergroup. Testing results are passed to a central controller. A layer groupwill be declared to have failed and will be automatically “mapped out”by the central controller if:—

[0269] 1). the layer group's self-test circuitry or external (to thelayer group) testing detects a fault that cannot be accommodated byonboard redundancy;

[0270] 2). the immediately or downstream upstream layer group detectsthat the layer group is not responding or not responding correctly tointerrogation, or

[0271] 3). power fails to the layer group.

[0272] The above list is not exhaustive and other circumstances mayrequire a layer group to be “mapped out”.

[0273] Failure of a layer group must not prevent communication betweenits adjacent layer groups and so communication between any two layergroups is not dependant on intermediate layer groups. The failure of alayer group should also not cause failure in the product being printedby that layer group when it fails.

[0274] Referring to FIGS. 10 to 18 there are schematically shown anumber of layer groups of a system 1000 designed for producing productswith up to n layers. Accordingly, the system 1000 has n active layergroups. The system has a series of spare layer groups 1012, 1013 & 1014that in ‘normal’ use are not used. These ‘spare’ layer groups arelocated downstream of the n^(th) active layer group 1011. In thedrawings, three ‘spare’ layer groups are shown. It will be appreciatedthat the number of spare layer groups may range from one upwards. Inthis system all layer groups, including spare layer groups arefunctionally identical.

[0275] For the purposes of explanation it is assumed that there is notransverse offsetting of odd and even layer groups and that an odd layercan be printed by an ‘even’ layer group and vice versa.

[0276] Each layer group, as discussed elsewhere, has onboard memory thatstores all the data necessary to define at least one layer. In theembodiment of FIGS. 10 to 18, each layer group has sufficient memory tostore data for three layers. For ease of explanation the drawings showeach layer group having three separate memory stores, represented by aseparate square in the drawings, labeled a, b & c, each representing thememory needed to store the data for one layer. Of course in practice,the memory may be continuous.

[0277] Each layer group stores data for the layer that it is presentlyprinting and for the two previous layers. Thus, layer group m storesdata for layer m, layer m−1 and layer m−2 in memory stores a, b and c,respectively. The data for each layer is represented in the drawings bythe code L_(n) in the memory squares, where n is the layer number. Thefirst layer group 1001 only stores data L₁ for the first layer, as ithas no upstream layer groups whilst the second layer group 1002 onlystores data L₁ & L₂ for the first and second layers. The indexes 1015above the boxes represent the layer being printed by each layer group.

[0278] The spare layer groups are physically identical to the otherlayer groups, but, as shown in the FIG. 10, only the first two spares1012 and 1013 are initially loaded with data. The first spare 1012 isinitially loaded with data L_(n) and L_(n−1) relating to layers n andn−1 in memory stores 1012 b and 1012 c. The second spare 1013 only hasdata L_(n) for layer n, stored in memory store 1013 c whilst the thirdspare 1014 and beyond, if any, initially have no data in memory.

[0279] The layer groups have data transfer links 1016 configured toenable layer data in the memory of one layer group to be transferred tothe two immediately adjacent active layer groups, i.e. an upstream and adownstream layer group. There may be one or more “inactive” layer groupsbetween active layer groups. Inactive layer groups are ignored by thesystem and the system is configured so that an inactive layer groupcannot affect operation of the system. Typically an inactive group isone that has suffered a failure that prevents it printing material asrequired. However, fully functional layer groups may be mapped out as‘inactive’ for other reasons.

[0280] Referring to FIG. 10 the initial configuration is shown and eachlayer group prints the corresponding layer, i.e. the first layer group1001 prints layer one, the second layer group 1002 prints layer two,etc.

[0281]FIG. 11 shows the situation where the fifth layer group 1005 hasbeen determined to have failed. The system maps out fifth layer group1005 and all layer groups downstream of layer group 1005 are instructedto print an earlier layer. Thus, layer group 1006 is instructed to printlayer five, layer group 1007 is instructed to print layer six and thenth layer group is instructed to print layer n−1. This is achieved bysending an ‘advance’ signal 1018 to all the downstream layer groups,preferably via the data link 1016 when a layer group fails. The advancesignal is also propagated to the ‘spare’ layer groups and so spare layergroup 1012 is instructed to print layer n.

[0282] This is possible as there is sufficient time between failurebeing detected and the substrate moving from one layer group to the nextlayer group and because each layer group already holds data defining anearlier layer. The time available to switch over is of the order of afew hundred milliseconds. Thus, the next layer group may finish off thepart completed layer printed by the upstream layer group. The layergroup 1004 now communicates directly with layer group 1006 and bypasseslayer group 1005, which is no longer active.

[0283] This switch over may be effectively instantaneous as all thelayer groups already hold data defining the previous layer. Thus, evenif layer group five fails part way through printing its layer, layergroup six may complete that layer as layer group six already holds datarelating to layer five. If there is sufficient gap between adjacentproducts, layer groups six onwards may complete printing of theirrespective layers before switching to an earlier layer. In thesecircumstances, layer group six would complete layer six on one product,complete the part completed layer five of the next product and thenprint layer five on subsequent products. Layer groups seven onwardswould complete their original layers and then switch to printing theearlier layers.

[0284] Referring to FIG. 12, layer group 1005 is now mapped out and alldownstream layer groups are ‘moved’ upstream one layer, i.e. layer group1006 becomes the fifth layer group, layer group 1007 becomes the sixthlayer group, layer group n becomes the (n−1)^(th) layer group and thefirst spare layer group 1012 is mapped as the n^(th) layer group.

[0285] At this time, each layer group downstream of the failed layergroup holds data relating to the layer it is now printing, the immediateupstream layer and the immediate downstream layer. Thus, layer group1006, now mapped as the fifth layer group, has data for layers four,five and six. The data for the immediate downstream layers is notrequired by any of the layer groups and so may be replaced.

[0286] Transfer of data between the layer groups now occurs via datalink 1016, as shown in FIG. 13. The data L₆ in layer group 1006 relatingto layer six is replaced with data L₃ relating to layer three. This dataL₃ is obtained from the immediate upstream layer group 1004 via datalink 1016.

[0287] Simultaneously, layer group 1006 transfers data L₄ relating tolayer four to layer group 1007 to replace the now redundant data L₈defining layer eight. A similar transfer occurs simultaneously for allthe layer groups downstream of the failed layer group, i.e. in an activelayer group previously mapped as layer group m+1 and now mapped as layergroup m, data relating to layer m+1 is replaced with data relating tolayer m−2 from layer group m−1. The first spare 1012, now mapped as then^(th) layer group, transfers data relating to layer n−1 to the secondspare 1013 and the third spare 1014, which originally held no data,receives data relating to layer n from layer group 1013. Simultaneoustransfer is possible because all the layer groups hold the necessarydata in memory. Whilst data for all n layers is transferredsubstantially simultaneously, the data link 1016 only carries data forone layer between adjacent layer groups. In addition, the switchover toaccommodate a failed layer group is not dependant on the completion ofthis data transfer. Thus, the capacity of the data link need not behigh.

[0288] Referring to FIGS. 14 & 15, assume layer group 1008, now mappedas the seventh layer group fails. A second ‘advance’ signal 1022 is sentto all active layer groups downstream of layer group 1008 to cause themto print the previous layer, as previously described i.e. layer group1009 synchronously takes over printing layer seven, the first spare 1012prints layer n−1 and the second spare 1013 prints layer n, with thethird spare 1014 still unused.

[0289] In the typical system approximately 10.6 Gbytes of data isrequired to define all the voxels of each layer and the transfer of thisamount of data takes some time. However, because each layer group holdsdata relating to two upstream layers, a failure of a layer group thatoccurs whilst the data transfers occurring will not be fatal.

[0290] Referring to FIG. 16, assume that the transfer of layer data as aresult of the failure of layer group 1008 is still occurring when layergroup 1003 fails. Thus data transfer 1022 is still occurring. A third‘advance’ signal 1024 is generated and sent to all active layer groupsdownstream of layer group 1003. Layer groups 1004, 1006 and 1007, nowmapped as layer groups four, five and six are not in the process ofreplacing data in their memory and can synchronously commence printinglayers three, four and five respectively. Although mapped layer groupsseven to n are in the process of replacing data in one memory store,they also already hold in memory data for the immediate upstream layer.Thus, layer group 1009 already holds data relating to layer six; theeighth layer group holds data for layer seven, all the way through tothe third spare 1014, which holds data for layer n. Thus all thedownstream layer groups already hold the necessary data and so all mayshift to printing the upstream layer whilst the first data transfer 1022is still occurring and on receipt of only an advance signal. This isshown in FIG. 17.

[0291] An additional instruction is issued to replace the data in eachlayer group m relating to layer m+1 with that relating to layer m−2.Accordingly, as shown in FIG. 17 layer group 1002 transfers data L₁relating to layer one to layer group 1004. Layer groups 1009 onwards,now mapped as layer groups six onwards, continue with the first datatransfer 1022, so that layer group data still populates one of itsmemory stores with data relating to earlier layers. The second datatransfer 1026 is commenced, preferably occurring simultaneously with thefirst transfer 1022, to transfer data relating to earlier layers.Depending on the capacity of the data link 1016, the second datatransfer may be delayed until the first transfer has completed. FIG. 18shows the layer data in the memory stores of the layer groups after thetwo data transfers have been completed.

[0292] Whilst the first data transfer is still occurring, layer groups1009 onwards do not hold a complete data set for an upstream layer. Assuch, if a fourth failure were to occur before the first data transferis completed the system has no layer redundancy. However, as soon as thefirst data transfer is complete all of the layer groups will hold datarelating to the current layer being printed and the immediate upstreamlayer, so restoring data redundancy for one failure. When the seconddata transfer completes the system is restored to having redundancy fortwo failures.

[0293] The system can thus cope with two failures occurring in the timeit takes to transfer data relating to one layer between the layergroups. If greater fault tolerance is required, it is merely a matter ofproviding more memory in each layer group. A system in which each layergroup can store data relating to i layers will be able to continue evenif i−1 failures occur in the time to transfer one layer's data betweenlayer groups.

[0294] If the number of spare layers is greater than i, the number ofspare layer groups does not affect the number of “simultaneous” failuresthat may occur before data transfer has completed. However, the numberof spare layer groups does effect the cumulative number of failures thatmay be accommodated before the manufacturing line needs to be stopped ina controlled manner for replacement of failed printhead or layer groups.It will be appreciated that in practice the number of spare layer groupsmaybe much greater than three.

[0295] In the embodiment shown in FIGS. 10 to 18 all of the layer groupsare identical, with a series of identical spare layer groups at thedownstream end of the n^(th) layer group. Where a production line doesnot have all layer groups identical, it will be appreciated that the oneproduction line may be treated as a series of smaller logical productionlines placed end on end, in which the layer groups of each logicalproduction line are identical. In this situation, spare layer groups maybe located at the downstream end of each logical production line andbefore the start of the next logical production line. It will also beappreciated that a non-identical layer group may replace a layer group,so long as the replacement is capable of printing all of the materialsprinted by the failed layer group. As an example, layer groups that onlyprint one or two materials can be replaced by downstream layer groupsthat can print eight materials, so long as the eight materials includethe first two.

[0296] In the system described, all layer groups can print both odd andeven layers. However, in some cases odd layer groups may not be able toprint even layers and even layer groups may not be able to print oddlayers. An example of such a case is where voxels are arranged in ahexagonal close pack arrangement and odd layer groups are physicallyoffset transversely relative to even layer groups.

[0297] In this case when a layer group fails, the next layer group wouldnot be able to print the previous layer and need to be mapped out. Thus,for example, if layer group five fails, both it and layer group sixwould be mapped out. Layer group seven would then print layer five andlayer group eight would then print layer six, and so on. Thus eachfailure would require the use of two spare layer groups and so twice asmany spare layer groups would be required to provide the ability to copewith the same number of failures. It follows that odd layer groups willstore data relating to odd layers and even layer groups will store datarelating to even layers. Thus layer group m will sore data relating tolayers m, m+2 and m+4. Apart from these differences, the system wouldfunction identically to that described.

[0298] As mentioned previously, a printhead may be able to successfullyprint material for one layer despite having one or more failed butunused nozzles. However, one or more failed nozzles may be required forprinting of earlier layers. As each layer group has memory for multiplelayers, it is possible at initialization, or at other times, todetermine if the printhead is capable of printing all the layers held inmemory, not just the layer being printed. The layer group may then holda status flag for the other layers indicating whether it is capable ofprinting them.

[0299] If a failure occurs in another printhead that requires the layergroup to print a layer that it cannot, the layer group may be mapped outas well. Effectively this would result in two simultaneous failures thatneeded to be accommodated. As such it may be desirable to increase thenumber of layers held in memory by each layer group.

[0300] It will be appreciated that this scenario has the potential toreduce the number of ‘failures’ and hence the number of spare layersrequired but at the same expense of requiring more memory to provide thesame level of simultaneous built in redundancy/fault tolerance.

[0301] Whilst the present invention has been described with reference tosemiconductor devices printing micron sized voxels, it is to beappreciated that the invention is not limited to the printing devicesdescribed or the voxel sizes described. Similarly, whilst preferredforms utilize about 1000 separate subsystems or layer groups, theinvention is not limited to systems having this many subsystems or layergroups.

[0302] Technologies currently exist that involve the (random) sprayingof molten metal droplets onto a former to form a metallic structure (seeU.S. Pat. No. 6,420,954 for an example). It is within the scope of theinvention to print or otherwise deposit droplets of metals havingmelting points significantly above that of semiconductor materials andin much larger drop sizes, for the formation of ‘bulk’ objects.

[0303] Many metal objects are cast or otherwise formed to a ‘rough’state. The rough casting is frequently then subject to various machiningprocesses to arrive at the finished article. Printing of metal objectsallows finished products to be produced without the need for suchmachining.

[0304] Preferred embodiments of the invention produce voxels of materialthat are substantially the same size, independent of location ormaterial. There is also a one to one relationship between voxels and‘droplets’, i.e. each voxel is constructed of one cured ‘droplet’ ofmaterial. Depending on the product, certain portions may not need to beproduced to the same fineness, such as the bulk layers of a casing.Accordingly these may be formed of larger droplets of materials.Accordingly different layer groups may have printheads printing the samematerials but in different drop sizes to produce either ‘super size’voxels or multiple ‘standard’ size voxels.

1. A three dimensional object creation system that prints objects layerby layer, the system including a plurality of printheads, the systemprinting at least part of each of multiple layers simultaneously,wherein the printheads are configured such that at least one of thelayers may be printed with a first set of materials and at least oneother of the layers may be printed with a second set of materials, andwherein the first and second sets are not the same.
 2. The system ofclaim 1 wherein the first set is a subset of the second set.
 3. Thesystem of claim 1 wherein each printhead only prints part or all of apredetermined layer.
 4. The system of claim 1 wherein the printheads aregrouped into layer groups, each layer group configured to print adifferent one of the multiple layers.
 5. The system of claim 1 whereinthe printheads are grouped into layer groups, each layer groupconfigured to print a different one of the multiple layers and whereinthe number of printheads in the layer groups is different.
 6. The systemof claim 1 wherein more than 100 layers are printed simultaneously. 7.The system of claim 1 wherein the printheads are grouped into layergroups, each layer group configured to print a different one of themultiple layers, and wherein at least one of the layer groups includes afirst set of nozzle groups, each nozzle group printing a materialdifferent to that printed by the other nozzle groups of the respectivelayer group, and at least one other of the layer groups includes asecond set of nozzle groups, each nozzle group printing a materialdifferent to that printed by the other nozzle groups of the respectivelayer group, and wherein the first and the second sets are not the same.8. The system of claim 7 wherein the first set of nozzle groups and thesecond set of nozzle groups include at least one nozzle group printingthe same material.
 9. The system of claim 7 wherein the first set ofnozzle groups print a first set of materials and the second set ofnozzle groups print at least the first set of materials.
 10. The systemof claim 7 wherein the nozzle groups include the same number ofprintheads.
 11. The systems of claim 7 wherein each nozzle groupincludes at least one row of nozzles.
 12. The system of claim 7 whereinat least one row of nozzles of at least two different nozzle groups areincorporated into a single printhead.
 13. The system of claim 7 whereineach printhead incorporates at least one nozzle row from only one nozzlegroup.
 14. The system of claim 7 wherein each printhead incorporates atleast one nozzle row from more than one nozzle group.
 15. A system asclaimed in claim 1 wherein the system includes a plurality ofprintheads.
 16. A system as claimed in claim 1 wherein each layer isdefined by a plurality of voxels arranged in a regular array and whereinthe voxels of each layer are printed so as to be offset by half a voxelrelative to the voxels of adjacent layers in a first direction, a seconddirection perpendicular to the first direction or both the first andsecond directions.
 17. A system as claimed in claim 1 wherein theprintheads are configured to enable printing of at least two differentmaterials in at least one layer.
 18. A system as claimed in claim 1wherein the system is configured to enable at least one first printheadthat is initially configured to print at least part of a first layer tobe dynamically reconfigured to print at least part of a second layer.19. A system as claimed in claim 1 wherein the system is configured toenable at least one first printhead that is initially configured toprint at least part of a first layer to be dynamically reconfigured toprint at least part of a second layer, and wherein if at least oneprinthead initially configured to print the second layer fails whilstprinting said second layer, said at least one first printhead isdynamically reconfigured to complete the printing of at least part ofsaid second layer.
 20. A system as claimed in claim 1 wherein the systemincludes semiconductor memory and wherein data defining at least onelayer is stored in the semiconductor memory.
 21. A system as claimed inclaim 1, the system executes a process, the system including a pluralityof subsystems, each of which performs a stage of the process, each ofthe subsystems configured to perform one of a first subset of N₁ of thestages, where N is greater than 1 and to change the stage of the subsetbeing performed on receipt of a change instruction; wherein, in theevent that one of the subsystems fails, at least one of the remainingsubsystems synchronously changes to performing the respective stage ofthe failed subsystem without requiring transfer of data relating therespective stage to the said at least one remaining subsystems, and whena subsystem changes to performing a different stage, the systemreconfigures the subsystem to be capable of performing a second subsetN₂ of the stages where N_(1 and N) ₂ have the same number of stages. 22.A system as claimed in claim 1 including a least two printheads, whereina first printhead is actively maintained at a first temperature and asecond printhead is actively maintained at a second temperature.
 23. Asystem as claimed in claim 1 including a least two printheads, a firstone of the printheads printing a first material and a second one of theprintheads printing a second material, the first material being cured bya first method and the second material being cured by a second methodand wherein the first and second methods are different.
 24. A system asclaimed in claim 1 including at least one printhead for printingmaterial to create a printed product, and an object incorporation devicethat incorporates inorganic semiconductors into the product beingprinted whilst the at least one printhead prints the product.
 25. Asystem as claimed in claim 1 including at least one object incorporationdevice that incorporates non-printed objects into partially completedproduct, the non-printed objects not being printed by the system.
 26. Asystem as claimed in claim 1 including an object incorporation devicethat inserts at least one non-printed object into at least one cavitycreated during the printing process, the object incorporation deviceincorporating the at least one non-printed object into the at least onecavity during the printing of the respective printed object.
 27. Asystem as claimed in claim 1 including at least one printhead thatprints electrical connections to at least one object incorporated in theproducts.